In the process of pre-curing polyimide (PI) used as a liquid crystal alignment layer, the evenness of the thickness of the PI may be unsatisfied due to differences among actual pre-curing conditions at various positions on a substrate. For example, in a region of the substrate where metallic wirings are intensive (such as a Vcom wiring region at an edge of a display pixel region), the actual temperature of its surface would be high. In the pre-curing process after the application of PI solution, the solvent in a region having a higher surface temperature is volatilized quickly. A level of PI solution after the volatilization is lowered and new PI solution will be supplemented immediately. Therefore, a height of the PI in the region where metallic wirings are intensive is locally higher than a normal value, while the height of the PI in the display pixel region at its edge is locally lower than the normal value. As a result, after pre-curing, a PI halation region (Halo region) may be formed in the region where metallic wirings are intensive, influencing a display effect.
FIG. 1 is a schematic view showing an alignment layer pre-curing device in the prior art. A pre-curing heating plate 1 is heated with uniform temperature, a substrate 2 has a metallic wiring region 3 provided thereon, and an alignment layer 4 is applied on the substrate 2. In the process of heating the pre-curing heating plate 1, the actual surface temperature of the metallic wiring region 3 is higher than the surface temperature of remaining region on the substrate 2, such that a PI halation region 5 may be formed in the former region. In the practical operation in the production line, unqualified products would have obvious PI halation phenomena in their metallic wiring regions. This has indicated that uniformly heating the pre-curing heating plate could not ensure the alignment layer on the substrate surface having various pattern designs is uniformly cured.